Observations of counter-propagating Alfvénic and compressive fluctuations in the chromosphere

Recent observations have found that chromospheric spicules behave like Alfvfluctuations. Low-frequency Alfvwaves are predicted to partially reflect in the transition region that has a gradient in the Alfv´ en speed, thereby producing inward Alfv´ en waves, which may interact nonlinearly with outward Alfvwaves to generate Alfv´ enic turbulence. However, the signature of Alfvturbulence in the chromosphere has not yet been quantitatively analyzed with observations. Here we an- alyze some characteristics related to Alfvturbulence with the observations from Hinode/SOT. We decompose the height-time diagram of the transverse oscillations to separate the outward and inward propagating Alfvsignals. The counter- propagating waves are found to have similar amplitude, period and phase speed, sug- gesting a state having an approximate balance in bi-directional energy fluxes. Counter- propagation of intensity oscillation with lower propagation speed is also presented, probably indicating the presence of slow mode waves. Moreover, we attempt to esti- mate the Elsspectra of the chromospheric turbulence for the first time. The rela- tive fluctuations in the magnetic field may be measured as the local slope of wave-like shapes in spicules. The resulting low-frequency Els¨ asser power spectra look similar to each other without showing a dominant population, which confirms these counter- propagating low-frequency Alfvwaves are in a state of balanced flux. These obser- vational results are believed to help us better understand the nature of chromospheric turbulence as well as chromospheric heating.